Leg prostheses can provide an artificial ankle, and artificial knee, or both an artificial ankle and an artificial knee. A transfemoral prosthesis is a prosthesis designed for above the knee amputees. Transfemoral prostheses are generally more complicated than transtibial prostheses, as they must include a knee joint. Such leg prostheses have been used successfully to restore mobility and freedom of many lower leg amputees. However, various issues still plague existing leg prostheses. One significant issue with existing leg prostheses is falls and far of falling among lower limb amputees. Approximately one in five lower limb amputees have reported sustaining an injury as a result of a fall within the last year, with about half of these lower limb amputees reporting that they have required medical attention.
Lower limb amputee falls are typically the result of the inability of state-of-the-art passive prostheses to provide proper joint kinetics and kinematics (particularly in conditions of uneven terrain). These limitations can severely compromise the standing and walking stability of the lower limb amputee (particularly of the transfemoral amputee), and thus increase the likelihood of a stumble or fall. Further, in the case of stumbling, these prostheses largely lack the ability to appropriately react (i.e., provide a recovery response), thus significantly increasing the likelihood that a stumble will result in a fall.